1. Field of the Invention
The present invention relates to a heat treatment apparatus and a method for heating a substrate in which impurities are implanted, such as a semiconductor wafer and a glass substrate for a liquid crystal display apparatus (hereinafter referred to simply as a “substrate”), by irradiating the substrate with light.
2. Description of the Background Art
In the manufacturing process for a semiconductor device, introduction of impurities is a required step for forming p-n junction in a semiconductor wafer. Currently, the introduction of impurities is generally performed by ion implantation and annealing performed thereafter. Ion implantation is a technique of ionizing elements of impurities such as boron (B), arsenic (As) and phosphorous (P) to collide with a semiconductor wafer at high acceleration voltage, to thereby physically implant impurities. The implanted impurities are activated by annealing treatment. In this case, if annealing time is not less than approximately several seconds, there is a fear that implanted impurities may be diffused deeply due to heat, whereby a junction depth becomes deep excessively, causing a problem in satisfactorily forming a device.
Therefore, an annealing method for heating a semiconductor wafer in an extremely short period of time is studied, and Japanese Patent Application Laid-Open No. 2007-281318 discloses activation of impurities implanted in a source/drain region using laser annealing (LSA). In addition, Japanese Patent Application Laid-Open No. 2008-98640 discloses activation of impurities through heating in a short period of time using flash lamp annealing (FLA).
Incidentally, a large number of defects are introduced into a silicon crystal of a semiconductor wafer as a result of implanting ions of high energy by ion implantation. Such defects tend to be introduced into a position which is slightly deeper than an ion implantation layer. In the case of performing annealing after the ion implantation, the introduced defects are desirably recovered also in conjunction with the activation of impurities.
However, in the case of performing heat treatment using laser annealing or flash lamp annealing for an extremely short period of time, for example, approximately several milliseconds, a temperature rise speed on a surface of a semiconductor wafer is faster than a speed at which heat is transmitted to an inside of the wafer due to heat conduction of silicon. Accordingly, though it is possible to raise temperature of an ion implantation layer, it is difficult to raise temperature sufficiently at a deep position into which defects are introduced. Naturally, when a semiconductor wafer is irradiated with light of extremely high energy, it is possible to raise temperature sufficiently at the deep position into which defects are introduced even by irradiation for an extremely short period of time, for example, approximately several milliseconds, to thereby recover the defects. However, surface temperature rises considerably to damage the semiconductor wafer, which leads to shattering of the semiconductor wafer in the worst case.
Moreover, in the case of performing annealing after the formation of a gate electrode, the gate electrode itself degrades by conventional irradiation for an extremely short period of time.